Drilling riser release method

ABSTRACT

The method of releasing a drilling riser depending from a surface vessel from a subsea installation, comprising unlatching a connector on the primary conduit of the drilling riser, allowing the tension in the drilling riser to cause a separation between the portion of the primary conduit above the connector and the portion of the primary conduit below the connector, and the separation causing one or more control lines to be cut into an upper portion and a lower portion.

TECHNICAL FIELD

This invention relates to the general subject of a releasing connection on a subsea drilling riser which will allow the escape of a drilling rig from a blowout situation when the primary control systems have failed.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable

BACKGROUND OF THE INVENTION

The field of this invention is that operating blowout preventers in deep water operations to seal the well bore and protect the environment in emergency situations when an obstruction is in the well bore. A surface rig is connected to the seafloor equipment by a drilling riser. When blowout conditions (the uncontrolled release of oil or gas) occur, the drilling riser becomes the conduit to deliver the oil and gas as fuel to a burning rig and can additionally anchor the rig to the seafloor. Assurance of release from the seafloor equipment can be extremely important.

Blowout preventer systems are major pieces of capital equipment landed on the ocean floor in order to provide a conduit for the drill pipe and drilling mud while also providing pressure protection while drilling holes deep into the earth for the production of oil and gas. The typical blowout preventer stacks have an 18¾ inch bore and are usually of 10,000 psi working pressure. The blowout preventer stack assembly weighs in the range of five hundred to eight hundred thousand pounds. It is typically divided into a lower blowout preventer stack and a lower marine riser package.

The lower blowout preventer stack includes a connector for connecting to the wellhead at the bottom on the seafloor and contains several individual ram type blowout preventer assemblies, which will close on various pipe sizes and in some cases, will close on an open hole with what are called blind rams. Characteristically there is an annular preventer at the top, which will close on any pipe size or close on the open hole.

The lower marine riser package typically includes a connector at its base for connecting to the top of the lower blowout preventer stack, it contains a single annular preventer for closing off on any piece of pipe or the open hole, a flex joint, and a connection to a riser pipe which extends to the drilling vessel at the surface.

The purpose of the separation between the lower blowout preventer stack and the lower marine riser package is that the annular blowout preventer on the lower marine riser package is the preferred and most often used pressure control assembly. When it is used and either has a failure or is worn out, it can be released and retrieved to the surface for servicing while the lower blowout preventer stack maintains pressure competency and remains at the wellhead on the ocean floor.

The riser pipe extending to the surface is typically a 21 inch O.D. pipe with a bore larger than the bore of the blowout preventer stack. It is a low pressure pipe and will control the mud flow which is coming from the well up to the rig floor, but will not contain the 10,000-15,000 psi that the typical blowout preventer stack will contain. Whenever high pressures must be communicated back to the surface for well control procedures, smaller pipes on the outside of the drilling riser, called the choke line and the kill line, provide this function. These will typically have the same working pressure as the blowout preventer stack and rather than have an 18¾-20 inch bore, they will have a 3-4 inch bore. There may be additional lines outside the primary pipe for delivering hydraulic fluid for control of the blowout preventer stack or boosting the flow of drilling mud back up through the drilling riser.

The blowout preventers are operated or closed in response to an electric signal from the surface to an electro-hydraulic control valve which directs fluid stored under pressure in accumulator bottles to the operating cylinders on the blowout preventer. Any number of events can prevent this sequence from occurring such as failure in the surface controls to send the signal, failure in the connecting lines from the surface to depth as great as 12,000′, failure of the electro-hydraulic valve to close, and absence of fluid stored under pressure.

All subsea blowout preventers have 100% redundant control systems to minimize the risk of non-operation. They are very characteristically called the yellow system and blue system and represent primary and secondary means to operate any function on the blowout preventer stack.

When all else fails, it is not necessary to have emergency operation of multiple components in the subsea blowout preventer stack. A single component—the blind shear rams can immediately secure an uncontrolled flow of oil or gas from the well. A flat faced gate from each side will meet at the middle to seal off the bore. If a pipe of any sort is in the bore at the time, it will simply shear the pipe in half and then seal. The blind shear ram is the ultimate safety device, but it must operate.

Ultimately, if all fails, there can be an uncontrolled release of oil and gas up the bore of the drilling riser with disastrous results on the surface vessel.

BRIEF SUMMARY OF THE INVENTION

The object of this invention is to provide a method of emergency release of the vessel from a subsea blowout preventer stack when the well is blowing out.

A second object of this invention is to close off the bottom of the released riser to prevent the release of the drilling mud to the environment.

A third object of this invention is to close off the bottom of the released riser to prevent the release of heavy drilling mud which can cause a collapse of the riser near the surface.

Another object of this invention is to provide for cutting of any pipe within the drilling riser to facilitate movement away from the cut riser portion,

Another object of this invention is to provide for cutting of control lines which are tying the vessel to the subsea blowout preventer stack.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a deepwater drilling system such as would use this invention

FIG. 2 is a view of the deepwater drilling system separated at the connection of the present invention.

FIG. 3 is a close-up view of the connection of the present invention in the normal drilling mode.

FIG. 4 is a close-up view of the connection of the present invention after being released.

FIG. 5 is a half section of the connection of the present invention in the normal drilling mode as was seen in FIGS. 1 and 3.

FIG. 6 is a half section of the connection of the present invention after being released as was seen in FIGS. 2 and 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a view of a complete system for drilling subsea wells 20 is shown in order to illustrate the utility of the present invention. The drilling riser 22 is shown with a central pipe 24, outside fluid lines 26, and control lines 28.

Below the drilling riser 22 is a flex joint 30, lower marine riser package 32, lower blowout preventer stack 34 and wellhead 36 landed on the seafloor 38.

Below the wellhead 36, it can be seen that a hole was drilled for a first casing string, that string 40 was landed and cemented in place, a hole drilled through the first string for a second string, the second casing string 42 cemented in place, and a hole is being drilled for a third casing string by drill bit 44 on drill string 46.

The lower blowout preventer stack 22 generally comprises a lower hydraulic connector for connecting to the subsea wellhead system 36, usually 4 or 5 ram style blowout preventers, an annular preventer, and an upper mandrel for connection by the connector on the lower marine riser package 32.

Below outside fluid line 26 is a choke and kill (C&K) connector 50 and a pipe 52 which is generally illustrative of a choke or kill line. Pipe 52 goes down to valves 54 and 56 which provide flow to or from the central bore of the blowout preventer stack as may be appropriate from time to time. Typically a kill line will enter the bore of the Blowout Preventers below the lowest ram and has the general function of pumping heavy fluid to the well to overburden the pressure in the bore or to “kill” the pressure. The general implication of this is that the heavier mud will not be circulated, but rather forced into the formations. A choke line will typically enter the well bore above the lowest ram and is generally intended to allow circulation to circulate heavier mud into the well to regain pressure control of the well.

Normal drilling circulation is the mud pumps 60 taking drilling mud 62 from tank 64. The drilling mud will be pumped up a standpipe 66 and down the upper end 68 of the drill string 46. It will be pumped down the drill string 46, out the drill bit 44, and return up the annular area 70 between the outside of the drill string 46 and the bore of the hole being drilled, up the bore of the casing 42, through the subsea wellhead system 36, the lower blowout preventer stack 34, the lower marine riser package 32, up the drilling riser 24, out a bell nipple 72 and back into the mud tank 64.

During situations in which an abnormally high pressure from the formation has entered the well bore, the thin walled drilling riser 24 is typically not able to withstand the pressures involved. Rather than making the wall thickness of the relatively large bore drilling riser thick enough to withstand the pressure, the flow is diverted to a choke line 26. It is more economic to have a relatively thick wall in a small pipe to withstand the higher pressures than to have the proportionately thick wall in the larger riser pipe.

When higher pressures are to be contained, one of the annular or ram blowout preventers are closed around the drill pipe and the flow coming up the annular area around the drill pipe is diverted out through choke valve 54 into the pipe 52. The flow passes up through C&K connector 50, up pipe 26 which is attached to the outer diameter of the riser 24, through choking means illustrated at 74, and back into the mud tanks 64.

On the opposite side of the drilling riser 24 is shown a cable or hose 28 coming across a sheave 80 from a reel 82 on the vessel 84. The cable 28 is shown characteristically entering the top of the lower marine riser package. These cables typically carry hydraulic, electrical, multiplex electrical, or fiber optic signals. Typically there are at least two of these systems, which are characteristically painted yellow and blue. As the cables or hoses 28 enter the top of the lower marine riser package 32, they typically enter the top of control pod to deliver their supply or signals. When hydraulic supply is delivered, a series of accumulators are located on the lower marine riser package 32 or the lower blowout preventer stack 34 to store hydraulic fluid under pressure until needed.

Release joint 90 has release joint upper portion 92 and release joint lower portion 94 are shown above flex joint 30 and contain components necessary to release the drilling riser 22 and vessel 84 from the subsea well 20 in emergency conditions.

Referring now to FIG. 2 release joint upper portion 92 is shown released from the release joint lower portion 94 and the vessel is shown as moving towards the right on the page. Drill string 46 is shown as cut, with a portion of the drill string 96 remaining inside the release joint lower portion 94. It can be noted that the remaining portion of the drill string 46 within the upper part of the drilling riser 22 has naturally moved upwardly because it was in tension.

Referring now to FIG. 3, release joint 90 is shown with an upper flange 100 engaging the lower flange 102 of a riser joint and lower flange 104 engaging the upper flange 106 of a riser joint 24 or the flex joint 30. A central connector 110 is shown and supports a cutter blade 112. A mating cutter blade 114 is mounted on an upper body 116. Control cable 120 is positioned between the cutter blades 112 and 114 by brackets at 122 and 124. An auxiliary line connection 130 is shown which illustrates what a choke line, a kill line, or a booster line might look like. Explosive or chemical cutter 132 is shown mounted on a pivot at 134.

Referring now to FIG. 4, release joint upper portion 92 is shown released from the release joint lower portion 94. Upper body 116 is raised above central connector 110 and valve restraining sleeve 140 is shown. Drill string 46 has been cut into upper portion 142 and lower portion 144 by explosive or chemical cutter 132 as it was released and pivoted down about pivot 134. Backstop 146 is seen opposite the bore from explosive or chemical cutter 132 as a safety precaution in case it is accidentally activated on the surface and personnel are in the area. Auxiliary connection 130 (illustrated in FIG. 3) is separated into a box member 150 and pin member 152. This is preferably a straight stab with seal which pulls out when the upper body 116 is raised. Control cable 120 is cut into upper portion 154 and lower portion 156. As a result of these separations and cuttings, the release joint upper portion 92 is released from the released joint lower portion 94 and therefore the vessel 84 (illustrated in FIG. 2) is free to move away from danger.

Referring now to FIG. 5, auxiliary line connection 130 is shown with a flapper valve 160 which is held open by the pin member 152. Upper body 116 is shown to house a finger valve 162 which is held in the open position by restraining sleeve 140. Explosive or chemical cutter 132 is held in a first position by the outer surface 164 of central connector 110. Firing mechanism 166 is a push button which is designed to not activate when explosive or chemical cutter 132 is engaged by outer surface 164. However, when firing mechanism engages a diameter smaller diameter than outer surface 164, it will cause the explosive or chemical cutter 132 to activate and cut the smaller diameter pipe. Central connector 110 pistons 170 and locking dogs 172 as are discussed in U.S. Pat. No. 6,609,734.

Referring now to FIG. 6, the central connector 110 has been released and release joint upper portion 92 is shown released from the release joint lower portion 94. Drill string upper portion 142 is shown as being moved higher within the release joint upper portion 92 as would be expected with the normal tension of the drill pipe. The absence of drill pipe from within the lower portion of the release joint upper portion 92 allows the finger valve 162 to close and trap the mud within the riser. Finger valve 162 is shown with 8 pie shaped finger sections 170 which have a metal core 172 for strength and area coated with rubber 174 for sealing. Each adjacent finger section 170 is engaged by a square profile 176 similar to a common wobble extension for a ratchet tool set to cause all sections to close together. Similarly, as the pin member 152 is removed from the box member 150, the flapper valve 160 will be allowed to close and trap the drilling mud within the auxiliary pipe.

At this time all connections between the upper portion of the drilling riser and the lower portion of the drilling riser have been released or severed, allowing the vessel to be moved to safety.

Line 180 brings hydraulic fluid from control valve 182 to unlatch central connector 110 and line 184 sends hydraulic fluid from control valve 182 to latch central connector 110. Hydraulic supply is preferably from one or more dedicated accumulators 186 so that their capacity cannot be depleted by other operations. Control valve 182 is moved to the unlatching position as shown by a spring 188 upon the loss of an electric signal to solenoid 190.

The signal can come along wire 192 from a control module 194 which is battery 196 powered so that it can be functional after all other control signals are lost. The control module 194 can be armed by the concurrent receipt of a signal from blue control system 196 along wire 198 and yellow control system 200 along wire 202. Blue control system 196 and yellow control system 200 are iconic of the control systems on every subsea blowout preventer system. When the arming signal is lost from both of the control systems, the control module 194 can go into a firing sequence. A typical sequence might be to send an alarming signal back through both control systems and back to the surface to notify that if it does not receive a disarm signal within 3 minutes, it will actuate control valve 182 and send fluid pressure from accumulators 186 to unlatch the central connector 110 as described above.

The non-obviousness of this invention is clearly demonstrated by the need for enhanced safety in emergency situations, the extended period over which the need has been known, and the lack of recognition of this solution to the problem.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. 

1. The method of releasing a drilling riser depending from a surface vessel from a subsea installation, comprising: unlatching a connector on the primary conduit of said drilling riser, allowing the tension in said drilling riser to cause a separation between the portion of said primary conduit above said connector and the portion of said primary conduit below said connector, and said separation causing one or more control lines to be cut into an upper portion and a lower portion.
 2. The method of claim 1 further comprising detecting the loss of one or more signals from said surface vessel.
 3. The method of claim 1 further comprising initiating a signal from said subsea installation to said surface vessel warning of impending release.
 4. The method of claim 1 further comprising said separation causing one or more auxiliary fluid lines to be separated into an upper portion and a lower portion.
 5. The method of claim 1 further comprising sealing the lower end of the upper portion of said one or more auxiliary lines.
 6. The method of claim 1 further comprising sealing the lower end of the upper portion of said primary conduit.
 7. The method of claim 1 further comprising activating a cutter to cut any pipe which is within said primary conduit.
 8. The method of claim 7 further comprising said cutter is an explosive cutter.
 9. The method of claim 7 further comprising said cutter is a chemical cutter.
 10. The method of claim 7 further comprising said cutter is not activated when engaging a circular body of a first diameter and is activated when engaging a circular body of a second diameter smaller than said first diameter.
 11. The method of releasing a drilling riser depending from a surface vessel from a subsea installation, comprising: unlatching a connector on the primary conduit of said drilling riser, allowing the tension in said drilling riser to cause a separation between the portion of said primary conduit above said connector and the portion of said primary conduit below said connector, and activating a cutter to cut any pipe which is within said primary conduit.
 12. The method of claim 11 further comprising said cutter is an explosive cutter.
 13. The method of claim 11 further comprising said cutter is a chemical cutter.
 14. The method of claim 11 further comprising said cutter is not activated when engaging a circular body of a first diameter and is activated when engaging a circular body of a second smaller diameter
 15. The method of claim 11 further comprising detecting the loss of one or more signals from said surface vessel.
 16. The method of claim 11 further comprising initiating a signal from said subsea installation to said surface vessel warning of impending release
 17. The method of claim 11 further comprising said separation causing one or more auxiliary fluid lines to be separated into an upper portion and a lower portion.
 18. The method of claim 11 further comprising sealing the lower end of the upper portion of said one or more auxiliary lines.
 19. The method of claim 11 further comprising sealing the lower end of the upper portion of said primary conduit.
 20. The method of claim 11 further comprising cutting one or more control lines or hoses which are outside said primary conduit.
 21. The apparatus of releasing a drilling riser depending from a surface vessel from a subsea installation, comprising: a connector for unlatching the primary conduit of said drilling riser, allowing the tension in said drilling riser to cause a separation between the portion of said primary conduit above said connector and the portion of said primary conduit below said connector, and one or more cutters for cutting said one or more control into an upper portion and a lower portion.
 22. The apparatus for releasing a drilling riser depending from a surface vessel from a subsea installation, comprising: a connector for unlatching the primary conduit of said drilling riser, allowing the tension in said drilling riser to cause a separation between the portion of said primary conduit above said connector and the portion of said primary conduit below said connector, and a cutter to be activated by said separation and then explosively or chemically cut any pipe which is within said primary conduit. 